1. Field of the Invention
The present invention relates to a pressure tank or prestressed cast iron pressure vessel which comprises a cylindrical tank shell body, a bottom, and a cover, which are composed of cast elements and are clamped together by means of axially extending prestressing cast steel elements, girders or braces arranged as tendons which are distributed over the circumference of the vessel body, have axes which are parallel to the axis of the vessel, and by means of tangentially prestressing steel elements located in channels on the outer surface of the vessel body; a pressure tank also comprises a steel liner which is anchored directly on the inner shell of the vessel body by means of a connection made of bolts with external threads and welded to the liner.
Within the framework of the present invention, the expression "cast element" refers to a structural element of cast metal, especially of cast iron or cast steel. With the heretofore known pressure tanks which are made into a cylindrical shell of cast elements, the structural differences are concentrated in the unsatisfactorily resolved problem of being able to fix or anchor a liner, which for sealing purposes or leak tightness is made of thin sheet steel and is not inherently stable as an independent structural part, directly on the cast elements of the tank shell body, i.e. without having to use a backfill between the liner and the cast shell. The difficulty of the liner anchoring is based on the one hand on criteria inherent to manufacture and assembly, and on the other hand on considerations regarding specific and definite boundary conditions of structural mechanics, especially for the analysis of strains due to the unbalanced forces in the liner plate, involved with a strength and quality insurance of the individual structual parts.
2. Description of the Prior Art
Among the heretofore known anchorings, elements having a variety of shapes are used, for example members having a T-profile, ribbed members which are provided with a compensating shaft, fishplate members, anchor plates provided with bolts, etc. Various stud bolts or bolt connections for anchoring the steel liner to the cast elements have also been proposed. In addition to welding onto the steel liner nuts, threaded bushes or screws, or screw bolts of conventional type in a more or less complicated configuration, it is also known to fasten by screw connection the steel liner to the cast elements using welded-on finned members or similarly profiled elements.
German Auslegeschrift No. 26 36 743 discloses a bolt connection according to which the steel liner is connected with the cast elements by means of so-called welding equipment and bolts which are welded onto intermediate liner sections.
The characteristic of all of these structural solutions is that, for reasons of manufacture and assembly, the liner anchoring is preferably disposed in the abutting areas of the cast elements. The drawback to this is that the liner, due to the number of anchorings, which is limited as a result of the localized distribution, unduly buckles during evacuation or cooling-off, as a result of which radially undefined force conditions in the wall of the cast elements are generated. Further drawbacks result from the shape of the predominantly one-sided sealing or tight welds and anchoring weldments or weld seams on the steel liner, whereupon difficulties arise during the welding-through and during the inspection of the weld seam connections. A further drawback is that the number of possible structural solutions for the anchoring of the liner to the cast elements is limited, since, due to the strength of the material and the reliability, only certain weld connections are allowed by the authorities as acceptable for pressure vessels.
It is an object of the present invention, while taking into consideration aspects of design, structure, production efficiency, assembly requirements, and economy, as well as permissible restrictions as allowed by the authorities, to optimally provide a cast-joint connection ahchor for a presuure tank of the aforementioned general type such that a steel liner thereof, which is disposed directly by means of a screw anchoring on the inner side of the tank shell body, which is built up of cast elements, at no position lifts-off from the cast elements as a result of varying pressure and heat conditions which occur during operation; furthermore, additional stressing of the screw anchoring is to be extensively avoided.
Several advantages are achieved with the pressure vessel of the present invention. The stepwise prefabrication of the cylindrical steel liner assures satisfactory connections, which are gas welded on both sides, to the sealing seams or tight welds of the sheet metal plates, and makes possible an all-around inspection of the structural members.
The steel liner is anchored on the innermost cylindrical shell, which is formed from the cast elements, at as many spots as desired without disturbance due to the axial and tangential prestressing tendons representing an important obJect of the invention. As a result of this anchoring, during cooling-off and evacuation operations, the stress is optimally taken over not only by the liner but also by the innermost cast element shell in their function as supporting stays. As a result, an undue lifting-off or buckling of the liner is avoided, and an additional stressing of the anchoring is extensively eliminated. The bracing or prestressing of the pressure tank shell body, which inventively is undertaken on the outer cylindrical shell, is in this way unaffected by these aforementioned stresses.